This invention relates to oceanographic instrumentation, and more particularly to autonomous devices which cycle vertically and repeatedly between the surface and a desired depth in the ocean.
To observe the ocean environment there is a class of deep submergence vehicles that move freely (no physical connection to surface or bottom). Some profile vertically between the surface and resting in stable equilibrium at depth, i.e., “profilers.” Others do not seek a stable equilibrium depth, instead they cycle vertically continuously, i.e., “gliders.” It is desirable that these vehicles, with their observational payload, be small and inexpensive. In the case of profilers, the vehicle should be capable of hundreds of profiles moving efficiently between a stable equilibrium depth, typically 2000 meters (m), and the surface over a period of several years. Gliders are in continuous motion and it is desirable to cycle vertically many hundreds of times with minimum work expended.
Commonly profiler and glider designs use a metal hull, typically an aluminum alloy, with an active buoyancy mechanism having a pump or displacer powered by an on-board energy supply. An example of a profiler is described in U.S. Pat. No. 6,807,856 (Webb). An example of a glider is described in U.S. Pat. No. 5,291,847 (Webb). Most cylindrical, metallic, pressure resistant hulls designed to operate at substantial depth have an increase in buoyancy as depth is increased, i.e., their compressibility is less than sea water.
The goal of the present invention is to minimize the energy required for vertical excursions by using a hull design in which the compressibility, pressure resistance, and buoyancy can be independently optimized.
The invention embraces two similar vehicle types. Those that have a static stable equilibrium at depth, commonly called profilers, and those that are in continuous vertical motion, typically gliders. Both vehicle classes benefit from a compressibility optimized for minimum energy expenditure and maximum buoyancy.